US20170045231A1 - Combustor burner arrangement - Google Patents

Abstract

A fuel lance for a burner of a combustor has a fuel lance body defining a fuel flow passage and a liquid fuel tip attached thereto and in flow communication with fuel flow passage. The liquid fuel tip has a fuel outlet and an array of air passages having outlets which are arranged outside a blank sector of a circumference around the fuel outlet, the blank sector defined by an angle from 30° to 160°. A burner includes the fuel lance and the igniter and a main air flow passage to direct at least a part of a main air flow over the fuel lance and over the igniter, the blank sector has a centre-line angled between +120° and −120° from a radial line from the axis and passing through the fuel lance. A method includes rotating the fuel lance between a start-up condition and a second condition.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• This application is the US National Stage of International Application No. PCT/EP2015/059444 filed Apr. 30, 2015, and claims the benefit thereof. The International Application claims the benefit of European Application No. EP14166841 filed May 2, 2014. All of the applications are incorporated by reference herein in their entirety.
FIELD OF INVENTION
• The present invention relates to combustion equipment of a gas turbine engine and in particular a liquid fuel lance for a burner arrangement of the combustion equipment, the burner arrangement and a method of operating the combustor equipment.
BACKGROUND OF INVENTION
• Gas turbines including dry low emission combustor systems can have difficulty lighting and performing over a full load range when using liquid fuels. Often this can be because of fuel placement and subsequent atomization of the fuel in mixing air flows particularly at low loads. Ideally, the fuel droplets need to be very small and injected into an appropriate part of the airflow entering the combustor's pre-chamber in the vicinity of a burner arrangement to burn in the correct flame location. Also the fuel droplets should not contact any wall surface but at the same time the fuel droplets need to come close enough to the igniter so that the igniter can ignite the vaporised fuel on start up. If the fuel droplets contact a surface this can lead to carbon deposits building up or lacquers forming and which can alter airflow characteristics or even block air and/or fuel supply holes.
• The liquid pilot injection lance can have additional air assistance to aid atomisation of the liquid fuel over a range of fuel flows. This air assistance can be a supplied via a number of air outlets completely surrounding a fuel orifice or filmer. This liquid pilot injection lance is in a region prone to liquid fuel contact and as a result tends to incur carbon deposits. These carbon deposits block the air assistance holes and subsequently prevent successful atomisation of the fuel. Poor atomisation of the pilot fuel also causes problems with ignition of the fuel at start-up. This is a common fault with gas turbine fuel injection systems and carbon build up is a common problem. Consequently, liquid pilot injection lances are regularly replaced and are considered a consumable part. This is undesirable because such replacement is expensive, causes the gas turbine to be off-line halting supply of electricity or power for example, and can be unscheduled.
SUMMARY OF INVENTION
• One objective of the present invention is to prevent carbon deposits forming on components. Another objective is to prevent carbon deposits forming on a fuel lance of a combustor. Another object is to improve the reliability of igniting the fuel in a combustor. Another objective is to improve the entrainment of fuel droplets in an air flow. Another objective is to improve the atomisation of liquid fuel in a combustor. Another objective is to prevent liquid fuel contacting a surface within the combustor. Another objective is to reduce or prevent scheduled or unscheduled shut down of the engine for maintenance attributed to replacing or cleaning combustor components subject to carbon deposits and particularly the liquid fuel lance.
• For these and other objectives and advantages there is provided a fuel lance for a burner of a combustor of a gas turbine combustor, the fuel lance has an axis and comprises a fuel lance body defining a fuel flow passage and a liquid fuel tip attached to the fuel lance body and in flow communication with the fuel flow passage, the liquid fuel tip comprises a fuel outlet and an array of air passages having outlets arranged about the fuel outlet, wherein the outlets are arranged outside a blank sector of a circumference around the fuel outlet, the blank sector is defined by an angle between and including 30° and 160° about the axis.
• The outlets may be arranged outside the blank sector defined by an angle of between 120° and 160° about the axis.
• The outlets may be arranged outside the blank sector defined by an angle of approximately 140° about the axis.
• In one example, there are eight outlets equally spaced about the fuel outlet and between one and three circumferentially adjacent outlets are blocked off to create the blank sector.
• In another aspect of the present invention there is provided a burner for a combustor of a gas turbine combustor, the burner comprises a burner body having a surface and an axis, a fuel lance, an igniter and a main air flow passage or passages, the fuel lance is at least partly housed within the burner body and comprises a liquid fuel tip having a fuel outlet and an array of air passages having outlets arranged about the fuel outlet, wherein the outlets are arranged outside a blank sector of a circumference around the fuel outlet, the blank sector is defined by an angle up to 160° about the axis, the outlets and the fuel outlet are located at or near to the surface, the igniter is at least partly housed within the burner body and has an end face, the end face is located at or near to the surface, the main air flow passage is arranged to direct at least a part of a main air flow over the fuel lance and then over the igniter, the blank sector has a centre-line and the centre-line is angled between +120° and -120° from a radial line from the axis and passing through the fuel lance.
• The main air flow passage or passages may be tangentially angled relative to the burner axis to create a clockwise or anticlockwise swirl direction of the main air flow, the air passages may be tangentially angled relative to a fuel lance axis to create a clockwise or anticlockwise swirl direction of the pilot air flow.
• The main air flow passage or passages and the air passages may be both tangentially angled in the same direction to create clockwise swirl direction of the main air flow and clockwise swirl direction of the pilot air flow or to create anticlockwise swirl direction of the main air flow and anticlockwise swirl direction of the pilot air flow, the centre-line of the blank sector is angled up to 60° from the radial line from the axis and passing through the fuel lance.
• The centre-line of the blank sector may be angled up to 20° from the radial line from the axis and passing through the fuel lance.
• The centre-line of the blank sector may be angled approximately 0° from the radial line from the axis and passing through the fuel lance. The term “approximately 0°” is intended to include 0° and relatively small non-zero angles which have the same or similar technical effect.
• The main air flow passage or passages and the air passages may be oppositely tangentially angled to create oppositely swirling main air flow and pilot air flow, the centre-line of the blank sector may be angled between 0° and 120° from the radial line from the axis and passing through the fuel lance.
• The igniter may be positioned downstream of the fuel lance with respect to the direction of the main air flow.
• In another aspect of the present invention there is provided a method of operating a burner for a combustor of a gas turbine combustor, the burner comprises a burner body having a surface and an axis, a fuel lance, an igniter and a main air flow passage or passages, the fuel lance is at least partly housed within the burner body and comprises a liquid fuel tip having a fuel outlet and an array of air passages having outlets arranged about the fuel outlet, wherein the outlets are arranged outside a blank sector of a circumference around the fuel outlet, the blank sector is defined by an angle up to 160° about the axis, the outlets and the fuel outlet are located at or near to the surface, the igniter is at least partly housed within the burner body and has an end face, the end face is located at or near to the surface, the main air flow passage is arranged to direct at least a part of a main air flow over the fuel lance and then over the igniter the blank sector has a centre-line and the centre-line is angled relative to a radial line from the axis and passing through the fuel lance, the burner further comprises a rotation mechanism arranged to rotate the fuel lance about its axis, the method comprises the step of rotating the fuel lance between a start-up condition and a second condition.
• At the start-up condition the blank sector may be angled between +120° and −120° from the radial line and at the second condition the blank sector may be angled between +240° and 0° from the radial line.
• The second condition may be any one of the group comprising weak extinction, part-load or maximum load.
• In one example, the fuel outlet is a fuel prefilmer and which may be divergent towards its end and can create a cone of fuel. In another example, the fuel outlet is an orifice and which can create a spray of fuel. In yet another example, the fuel outlet is a number of orifices and each orifice can create a spray of fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
• Further features, properties and advantages of the present invention will become clear from the following description of embodiments in conjunction with the accompanying drawings.
• FIG. 1 shows part of a turbine engine in a sectional view in which the present invention is incorporated,
• FIG. 2 shows a perspective schematic view of a section of a combustor unit of turbine engine and in detail a burner arrangement including a pilot burner surrounded by a main burner, the pilot burner having a liquid fuel lance and an igniter and is in accordance with present invention,
• FIG. 3 shows a schematic perspective and cut-away view of part of the pilot burner and in detail the liquid fuel lance in accordance with present invention,
• FIG. 4 is a view along a combustor axis and onto the surface of the burner where the pilot burner is generally surrounded by the main burner in accordance with present invention,
• FIG. 5 andFIG. 6 show sectional views of the main air flow along paths A-A and B-B respectively as shown inFIG. 4 and illustrates respective distributions of fuel droplets issuing from the liquid fuel lance,
• FIG. 7 is a view on a tip of a known liquid fuel lance and generally along its axis showing an array of outlets arranged symmetrically around a fuel outlet; the array of outlets directs a pilot air flow to impinge on, shearing and atomizing a liquid fuel film,
• FIG. 8 is a view on a tip of the liquid fuel lance and generally along its axis showing an array of outlets arranged asymmetrically around a fuel outlet; a blank sector having no outlets can be seen, this asymmetric arrangement of outlets is in accordance with the present invention,
• FIG. 9 is a view on the surface of the burner and along the burner's central axis and indicates the orientation of the liquid fuel lance relative to the main air flow from the main burner and relative to the burner's central axis and in accordance with the present invention,
• FIG. 10 is a schematic illustration on to the surface of the burner and including a first mechanism capable of rotating the liquid fuel lance about its own axis such that the blank sector can be orientated during different modes of operating the combustor and is in accordance with the present invention,
• FIG. 11 is a schematic illustration of a section through a gas turbine engine showing the burners of the combustor units mounted around the engine and including a second mechanism capable of rotating the liquid fuel lances about their own axes such that the blank sector can be orientated during different modes of operating the combustor and is in accordance with the present invention.
DETAILED DESCRIPTION OF INVENTION
• FIG. 1 shows an example of agas turbine engine10 in a sectional view and generally arranged about alongitudinal axis20. Thegas turbine engine10 comprises, in flow series, aninlet12, acompressor section14, acombustor section16 and aturbine section18 which are generally arranged in flow series and generally in the direction of the longitudinal orrotational axis20. Thegas turbine engine10 further comprises ashaft22 which is rotatable about therotational axis20 and which extends longitudinally through thegas turbine engine10. Theshaft22 drivingly connects theturbine section18 to thecompressor section12. Thecombustor section16 comprises an annular array ofcombustor units16 only one of which is shown.
• In operation of thegas turbine engine10, air24, which is taken in through theair inlet12 is compressed by thecompressor section14 and delivered to the combustion section orunit16. Thecombustor unit16 comprises aburner plenum26, a pre-chamber29, acombustion chamber28 defined by a doublewalled can27 and at least oneburner30 fixed to eachcombustion chamber28. The pre-chamber29, thecombustion chamber28 and theburner30 are located inside theburner plenum26. Thecompressed air31 passing through thecompressor12 enters adiffuser32 and is discharged from thediffuser32 into theburner plenum26 from where a portion of the air enters theburner30 and is mixed with a gaseous and/or liquid fuel. The air/fuel mixture is then burned and the resultingcombustion gas34 or working gas from the combustion chamber is channelled via atransition duct35 to theturbine section18.
• Theturbine section18 comprises a number of blade carryingrotor discs36 attached to theshaft22. In the present example, twodiscs36 each carry an annular array ofturbine blades38. However, the number of blade carrying rotor discs could be different, i.e. only one disc or more than two rotor discs. In addition, guidingvanes40, which are fixed to astator42 of thegas turbine engine10, are disposed between theturbine blades38. Between the exit of thecombustion chamber28 and the leadingturbine blades38inlet guiding vanes44 are provided.
• Thecombustion gas34 from thecombustion chamber28 enters theturbine section18 and drives theturbine blades38 which in turn rotates theshaft22 to drive thecompressor section12. The guidingvanes40,44 serve to optimise the angle of the combustion or working gas on to theturbine blades38. Thecompressor section12 comprises an axial series of guide vane stages46 and rotor blade stages48.
• The terms upstream and downstream refer to the flow direction of the airflow and/or working gas flow through the engine unless otherwise stated. The terms forward and rearward refer to the general flow of gas through the engine. The terms axial, radial and circumferential are made with reference to therotational axis20 of the engine unless otherwise stated.
• FIG. 2 is a perspective view of a part of thecombustor16 showing theburner30, the pre-chamber29 and part of thecombustion chamber28. Thecombustion chamber28 is formed with a tubular-like shape by the double walled can27 (shown inFIG. 1) having and extending along acombustor axis50. Thecombustor16 extends along the combustor axial50 and comprises the pre-chamber29 and themain combustion chamber28, wherein the latter extends in acircumferential direction61 around thecombustor axis50 and generally downstream, with respect to the gas flow direction, of thepre-chamber volume29.
• Theburner30 comprises apilot burner52 and amain burner54. Thepilot burner52 comprises aburner body53, aliquid fuel lance56 and anigniter58. Themain burner54 comprises aswirler arrangement55 having an annular array ofswirler vanes60 definingpassages62 therebetween. The annular array ofswirler vanes60 are arranged generally about aburner axis50, which in this example is coincident with thecombustor axis50, and in conventional manner. Theswirler arrangement55 includes main fuel injection ports which are not shown, but are well known in the art. Themain burner54 defines part of the pre-chamber29. Thepilot burner52 is located in anaperture57 and generally radially inwardly, with respect to the burner/combustor axis50, of themain burner54. Thepilot burner52 has asurface64 that defines part of an end wall of the pre-chamber29. The end wall is further defined by themain burner54.
• Theliquid fuel lance56 is at least partly housed in afirst hole66 defined in theburner body53 of thepilot burner52. A pilotair flow passage69 is formed between theliquid fuel lance56 and the walls of thefirst hole66. Theliquid fuel lance56 comprises an elongatefuel lance body86 and aliquid fuel tip72. The elongatefuel lance body86 is generally cylindrical and defines afuel flow passage70. Theliquid fuel tip72 is mounted at one end of the elongatefuel lance body86 and is located near to or at thesurface64. Theliquid fuel lance56 will be described in more detail with reference toFIG. 3. Theigniter58 is housed in asecond passage74 defined in theburner body53 of thepilot burner52. The end of theigniter58 is located near to or at thesurface64. Theigniter58 is a well known device in the art and that requires no further description. Inother combustors16 it is possible that more than one liquid fuel lance and/or more than one igniter may be provided.
• During operation of the gas turbine engine and more particularly at engine start-up, a starter-motor cranks the engine such that thecompressor14 andturbine16 are rotated along with theshaft22. Thecompressor14 produces a flow ofcompressed air34 which is delivered to one or more of thecombustor units16. A first or major portion of thecompressed air34 is amain air flow34A which is forced through thepassages62 of theswirler arrangement55 where theswirler vanes60 impart a swirl to thecompressed air34 as shown by the arrows. A second or minor portion of thecompressed air31 is apilot air flow34B which is forced through the pilotair flow passage69. Thepilot air flow34B can also be referred to as an air assistance flow.Liquid fuel76 is forced through thefuel flow passage70 and is mixed with thepilot air flow34B and themain air flow34A in order to atomise the liquid fuel. Atomisation of the liquid fuel into very small droplets increases surface area to enhance subsequent vaporisation.
• Themain air flow34A generally swirls around thecombustor axis50. The swirler vanes60 impart a tangential direction component to themain air flow34A to cause the bulkmain air flow34 to have a circumferential direction of flow. This circumferential flow aspect is in addition to the general direction of the air and fuel mixture along thecombustor axis50 from or near thesurface64 towards the transition duct35 (seeFIG. 1). The fuel and air mixture passes through the pre-chamber29 and into thecombustion chamber28. Themain air flow34A forces thepilot air flow34B and entrained fuel near to theigniter58, which then ignites the fuel/air mixture.
• To start the engine, a starter motor rotates theshaft22,compressor14 andturbine18 to a predetermined speed when the pilot fuel is supplied and ignited. Once ignited the combustor internal geometry and the air flow patterns cause a pilot flame to exist. As the engine becomes self-powering the starter-motor can be switched off. As engine demand or load is increased from start-up, fuel is supplied to the main fuel injection ports and mixed with themain air flow34A. A main flame is created in thecombustion chamber28 and which is radially outwardly located relative to the pilot flame.
• Reference is now made toFIG. 3, which shows a schematic perspective and cut-away view of part of thepilot burner52 and in detail theliquid fuel lance56. Theliquid fuel lance56 comprises the elongatefuel lance body86 and theliquid fuel tip72 which are elements that can be unitary or separate. Theliquid fuel tip72 is located and captured by a narrowing78 at an end of thefirst hole66 and forms a tight fit. At the end of thefuel flow passage70, theliquid fuel tip72 includes aswirl plate80 which defines an array offuel conduits82 having inlets and outlets. Thefuel conduits82, only one of which is shown, are angled relative to a longitudinal orfuel lance axis79 of theliquid fuel lance56. Downstream of theswirl plate80 is afuel swirl chamber84 and then afuel outlet86, which in this example is a fuel filmer. Thisfuel filmer86 is divergent and produces a cone of liquid fuel. In other examples, thefuel outlet86 can be an orifice that produces a spray of fuel or a number of orifices, each producing a spray of fuel.
• Theliquid fuel tip72 forms an array of pilotair flow conduits88 having inlets that communicate with the pilotair flow passage69 andoutlets90 which surround thefuel filmer86. In this exemplary embodiment, the pilotair flow conduits88 are inclined or angled in both a circumferential sense and a radially inwardly relative to thelongitudinal axis79 of theliquid fuel lance56. In other embodiments, the pilotair flow conduits88 may be axially aligned, or angled in only one of the circumferential sense or radially inwardly relative to thelongitudinal axis79. In this exemplary embodiment there are 8 pilotair flow conduits88; although in other embodiments there may be more or fewer conduits.
• Pilot liquid fuel flowing in thefuel flow passage70 enters the inlets of thefuel conduits82 and exits the outlets imparting a swirl to the fuel in thefuel swirl chamber84. The swirling fuel forms a thin film over thefuel filmer86, which sheds the fuel in a relatively thin cone.Pilot air flow34B impinges the cone of fuel and breaks the fuel into small droplets. The swirling vortex of air from theoutlets90 atomises the fuel along with themain air flow34A.
• Thepilot air flow34B is particularly useful at engine start-up and low power demands when themain air flow34A has a relatively low mass flow compared to higher power demands and because of the lower mass flow is less able to atomise the liquid fuel. Advantageously, thepilot air flow34B provides cooling to the pilot fuel lance and helps prevent fuel coking and carbon build up on the pilot fuel lance.
• FIG. 4 is a view along thecombustor axis50 and on thesurface64 of theburner30 where thepilot burner52 is generally surrounded by themain burner54. Theliquid fuel lance56 and theigniter58 are shown mounted in theburner body53 of thepilot burner52. Theswirler arrangement55 of themain burner54 surrounds thesurface64 and directs themain airflow34B via the annular array ofpassages62. The annular array ofswirler vanes60 andpassages62 are arranged to impart a tangential flow component to themain air flow34A such that when the airflow portions from eachpassage62 coalesce they form avortex34C generally about theburner axis50. In this embodiment, thevortex34C rotates generally anti-clockwise as seen inFIG. 4; thisvortex34C could also be said to be rotating in a clockwise direction as it travels in a direction from thesurface64 to thetransition duct35 through the pre-chamber29 and then thecombustor chamber28.
• In this exemplary embodiment, thevortex34C is a single vortex, but in other examples the arrangements ofpilot burner52 and themain burner54 can create a number of vortices rotating in either the same direction or different directions and at different rotational speeds.
• The positions of theliquid fuel lance56 and theigniter58 are arranged so that the swirling or rotatingmain air flow34A passes over or around theliquid fuel lance56 and then on to theigniter58. As the main airflow forms avortex34C about theaxis50, theliquid fuel lance56 and theigniter58 are positioned at approximately the same radial distance from theaxis50. Thus as thefuel lance56 injects or sprays liquid fuel into the pre-chamber29 themain airflow34C entrains the fuel and transports it towards theigniter58, where ignition can take place.
• Thevortex34C has many different stream velocities within its mass flow. In this example, the portion of the vortex denoted by arrow34Cs is travelling at a lower velocity than the portion of the vortex denoted by arrow34Cf. Main air flow portion34Cs is radially inwardly of main air flow portion34Cf with respect to theaxis50. Main air flow portion34Cs is at approximately the same radial position as the radially inner part of thepilot fuel lance56 and the main air flow portion34Cf is at approximately the same radial position as the radially outer part of thepilot fuel lance56.
• FIG. 5 andFIG. 6 show sectional views of the main air flow along paths A-A and B-B respectively as shown inFIG. 4 and the distribution of fuel droplets. InFIG. 4 the flow path B-B is radially outwardly of thefuel lance56 andigniter58 and the flow path A-A is approximately at the same radius as at least a part of thefuel lance56 andigniter58.
• InFIG. 6 thefuel lance56 andigniter58 are shown in dashed lines for reference purposes. As shown, each portion of main air flow exiting eachpassage62 flows for a short distance immediately across thesurface64, before leaving thesurface64 and travelling away from thesurface64 and along theaxis50 as another portion of the main air flow joins from a circumferentiallyadjacent passage62. Thus as can be seen the anyfuel droplets92 entrained in this portion of the main air flow long flow path B-B are quickly lifted away from thesurface64 and therefore away from theigniter58.
• InFIG. 5 themain air flow34A passes over thefuel lance56 and on towards theigniter58. Theoutlets90, which surround thefuel filmer86 of thefuel lance56, direct thepilot air flow34B to impinge on the cone of fuel exiting thefuel filmer86 and break the fuel film intosmall droplets92. The swirling vortex of pilot air, shown schematically as94, from theoutlets90 atomises the fuel as it mixes with themain air flow34A. The swirling vortex ofpilot air94 effectively forms a fluid buffer and causes to be formed on its leeward or downstream side a recirculation zone or a low-pressure zone96. This recirculation zone or a low-pressure zone96 draws themain air flow34A towards thesurface64 between thefuel lance56 andigniter58. A portion of thefuel droplets92 are also drawn towards thesurface64 and therefore close to theigniter58 such that good ignition of the fuel/air mixture is possible.
• Referring now toFIG. 7, which is a view on thetip72 of thefuel lance56 and generally along itsaxis79, the array ofoutlets90 direct thepilot air flow34B with a tangential component. When the portions ofpilot air flow34B from eachoutlet90 merge they coalesce into thepilot vortex94. Thepilot vortex94 rotates in a generally anti-clockwise direction as seen inFIG. 7; thisvortex94 could also be said to be rotating in a clockwise direction as it travels in a direction from the surface of thetip72 towards thetransition duct35 through the pre-chamber29 and then thecombustor chamber28. In one example, there are 8outlets90 arranged symmetrically about theaxis79 of the fuel lance and about thefuel filmer86. This arrangement of outlets produces, at least initially, asymmetric pilot vortex94.
• However, in service it has been found that theoutlets90 become blocked by carbon deposits formed from liquid fuel landing on the surfaces of thefuel lance56. This blocking reduces the amount ofpilot air flow34B which in turn this reduces the effectiveness of thepilot air flow34B shearing and breaking up the fuel film. As a consequence ignition of the fuel/air mixture becomes more difficult and unpredictable. Thus it has been found that the symmetry of thepilot vortex94 causes particular air flow characteristics that lead to liquid fuel contacting the surface of the fuel lance and which then forms carbon deposits that block theoutlets90.
• InFIG. 8 is a view on thetip72 of thefuel lance56 and generally along itsaxis79, the array ofoutlets90 direct thepilot air flow34B with a tangential component. In this example, 3 of theoutlets90 have been fully blocked off in ablank sector98. Theblank sector98 is defined by an angle θ about the fuel lance'saxis79. In this example the angle θ is approximately 140° and for other examples, the angle θ can be between and including 30° and 160°. Angles between 60° and 160° are more favourable and produce an asymmetric fuel/air vortex94 which is readily broken up by the main air flow. Essentially these angles for theblank sector98 relate to at least one and up to three outlets being blocked off. However, as should be appreciated any other design of fuel lance may incorporate more orless outlets90 than the eight shown in this exemplary embodiment. The term ‘blocked off’ can mean that either theoutlets90 that exist are sealed, by welding or an insert for example, or by not forming some of thepassages88 andoutlets90 during manufacture of a new fuel lance. A centre-line100 is shown inFIG. 8 and which is the centre-line or bisector of theblank sector98 to define the orientation of thefuel lance56 andblank sector98 relative to thecombustor chamber axis50.
• This arrangement creates an asymmetricpilot air flow34B delivery and hence anasymmetric pilot vortex94. Thisasymmetric pilot vortex94 has the effect of keeping thefuel lance56 free from liquid fuel landing on its surfaces and subsequent carbon deposits by creating an air flow regime around the pilot lance that shields thepilot lance56 fromdroplets92. This has the benefit that the pilotair flow outlets90 do not block during use and therefore the quality of the fuel spray and atomization is maintained. Consequently, ignition at start-up is also improved. In addition, the pilot air flow or ‘air assistance’ being asymmetric increases the local turbulence and improves the shear on thedroplets92, aiding their atomization and pushing thedroplets92 away from theoutlets90, preventing any carbon build up due to the liquid fuel coming into contact with the injector surface.
• The asymmetricpilot air flow34B delivery and theasymmetric pilot vortex94 remain strong enough to effectively form thefluid buffer94 and cause to be formed on its leeward or downstream side, therecirculation zone96 or low-pressure zone96. Thus therecirculation zone96 or low-pressure zone96 still draws themain air flow34A towards thesurface64 between thefuel lance56 andigniter58. A portion of thefuel droplets92 are also drawn towards thesurface64 and therefore close to theigniter58 such that good ignition of the fuel/air mixture remains equally possible.
• It has been found that theasymmetric pilot vortex94 is able to prevent or substantially preventliquid droplets92 contacting the surfaces of thefuel lance56 whatever the orientation of the centre-line100 of theblank sector98. However, there is only a significant benefit to the delivery offuel droplets92 in the main flow to theigniter58, as described above, if the orientation of the centre-line100 is in a particular orientation compared to thevortex34C or relative to thecombustor chamber axis50.
• The air from theair passages88 immediately impinges on the liquid fuel issuing from thefuel outlet86, which is to say that there may be no other air passages or outlets between thefuel outlet86 and theair passages88. Thus the fuel/air vortex94 may be created by only the fuel from the fuel outlet and the air from the air passages. Thus it is the combination of the fuel from the fuel outlet and the air from the air passages that creates theasymmetric pilot vortex94.
• Referring toFIG. 9 which is a view on thesurface64 of theburner30 and along theaxis50 and from which aradial line102 emanates and passes through theaxis78 of thefuel lance56. Thefuel lance56 andigniter58 are shown along withmain airflow arrows34A issuing from the mainair flow passages62. As described earlier, the portion of the vortex denoted by arrow34Cf is travelling at a generally higher velocity than the portion of the vortex denoted by arrow34Cs. The relatively slower flow is generally radially inward of the faster velocity air.
• Thefuel lance56 as previously described is at least partly housed within theburner body53 of theburner30 and theoutlets90 and thefuel filmer86 are located at or near to thesurface64. In this example, theoutlets90 and thefuel filmer86 are located below thesurface64 in theburner body53. Theigniter58 is also at least partly housed within theburner body53 and has anend face59, located just below thesurface64, but could be at or near to thesurface64.
• Theburner30 further includes an array ofgas injection ports122 generally formed in a radially outward part of theburner30 and under acircumferential lip124 as shown inFIG. 2. Thesegas injection ports122 can supply a pilot gas-fuel as is known in the art.
• The terms clockwise and anticlockwise are with respect to the view on thesurface64 of theburner30 as seen inFIG. 9.
• In this exemplary embodiment, the centre-line100 of theblank sector98 and is angled at approximately 0° relative to theradial line102 extending from thecombustor chamber axis50 to thefuel lance axis78. Furthermore, the main air flow passages are tangentially angled relative to theburner axis50 to create an anticlockwise swirl direction of themain air flow34A and theair passages88 are tangentially angled relative to thefuel lance axis79 to create an anticlockwise swirl direction of thepilot air flow34B. However, in this first embodiment the range of angles which provide at least some of the desired advantages of the present invention is between and including +60° and -60°. The most advantageous range of angles is between and including +20° and −20°.
• In a second embodiment, the main air flow passages are tangentially angled relative to theburner axis50 to create an anticlockwise swirl direction of themain air flow34A and theair passages88 are tangentially angled relative to thefuel lance axis79 to create a clockwise swirl direction of thepilot air flow34B. In this second embodiment the range of angles which provide at least some of the desired advantages of the present invention is between and including +120° and 0°.
• In a third embodiment, the main air flow passages are tangentially angled relative to theburner axis50 to create a clockwise swirl direction of themain air flow34A and theair passages88 are tangentially angled relative to thefuel lance axis79 to create an anticlockwise swirl direction of thepilot air flow34B. In this third embodiment the range of angles which provide at least some of the desired advantages of the present invention is between and including 0° and -120°.
• Thus overall, the centre-line100 of theblank sector98 and can be angled between +120° and −120° from aradial line102 from theaxis50 and passing through thefuel lance56. In all embodiments, theigniter58 is positioned downstream of thefuel lance56 with respect to the clockwise or anticlockwise direction of themain air flow34A.
• The orientation of thefuel lance56 as described above is advantageous in that theoutlets90 are kept free of carbon deposits and therefore good atomisation of the fuel film and good start-up ignition is maintained. During ignition it is important that fuel washes over theigniter58 to ensure reliable ignition. However, during other engine conditions such as weak extinction, part-load or maximum load other orientations of theblank sector98 are even more beneficial. During normal engine running, at engine speed or power above ignition or start up, it is desirable to avoid the fuel contacting or washing over theigniter58 because it may form carbon deposits. Thus at ignition the condition described with reference toFIG. 5 is desirable where the fuel droplets wash over or very close to the injector; and during normal engine running it is desirable that the condition described with reference toFIG. 6 is desirable where the fuel droplets are generally carried away from the igniter.
• Thus a method of operating theburner30 in accordance with the present invention comprises the step of rotating the fuel lance between a start-up condition and a second condition. The second condition can be any one of the conditions such as weak extinction, part-load or maximum load. In particular, weak extinction is a condition where the flame can extinguish if there is further decrease in fuel supply and is related to flame stability. For the same fuel/air ratio with a lower weak extinction, the flame is less likely to extinguish.
• Referring back toFIG. 8 and its description, theblank sector98 has the centre-line100 angled or orientated relative to theradial line102; at engine start-up condition theblank sector98 is angled between +120° and −120° from theradial line102 and at the second condition theliquid fuel lance56 is rotated about itsown axis79 such that theblank sector98 is angled between +240° and −360° from theradial line102. Thus in one example, at start-up the centre-line102 is angled at approximately 0° from theradial line102 and a high-power condition, theliquid fuel lance56 is rotated by approximately −120° as viewed inFIG. 8.
• In order to rotate the fuel lance56 a rotation mechanism is provided and two examples are described with reference toFIG. 10 andFIG. 11.
• FIG. 10 is a schematic illustration on to the surface of theburner30 and includes afirst mechanism104 capable of rotating theliquid fuel lance56 about itsown axis79 such that theblank sector98 can be orientated to different positions during different modes of operating the combustor and/or engine. Thefirst mechanism104 comprises anactuator106 having adrive rod108 connected via alinkage110 to thefuel lance56. Thefuel lance56 may be mounted to theburner30 via suitable bearings. Thefirst mechanism104 is capable or rotating the fuel lance between afirst orientation112 and asecond orientation114 shown schematically by the dashed lines. Eachburner30 is equipped with afirst mechanism104 and eachfirst mechanism104 is connected to anelectronic controller116. Theelectronic controller116 sets the rotational position of theactuator106 dependent on the engine or combustor condition. Theelectronic controller116 may be a main engine controller or a stand-alone device. In this example, it is possible to independently orientate eachliquid fuel lance56 and depending on each combustor units' demanded output or condition.
• FIG. 11 is a schematic illustration of a section through thegas turbine engine10 showing the array ofburners30 of thecombustor units16 mounted around the engine and including asecond mechanism120 capable of rotating the liquid fuel lances56 about their own axes such that the blank sector can be orientated to different positions during different modes of operating the combustor. In this example, like components have been give the same reference numerals and operate in a generally similar manner and will not be describe again. In this example, thesecond mechanism120 includes anactuation ring118 to which theactuator rod108 is connected and to which eachliquid fuel lance56 is drivingly connected for rotation about its own axis. In this example, all of the liquid fuel lances56 are rotated simultaneously and depending on the combustion systems' demanded output or condition.
• It should be appreciated that theliquid fuel tip72 is attached to thefuel lance body68 in such a way that in service they are rigidly connected and cannot move relative to one another. However, theliquid fuel tip72 may be removed from thefuel lance body68 for servicing or replacement. Such a removable attachment may be achieved via cooperating screw threads or a bayonet fitting. Further, theliquid fuel tip72 andfuel lance body68 may be welded together or made integral, such as by casting.

Claims (17)

What is claimed is:

1. A fuel lance for a burner of a combustor of a gas turbine, the fuel lance has an axis and comprises:

a fuel lance body defining a fuel flow passage and

a liquid fuel tip attached to the fuel lance body, the liquid fuel tip comprises a fuel outlet and an array of air passages having outlets arranged about the fuel outlet, fuel flows through the fuel flow passage and liquid fuel tip and issues from the fuel outlet

wherein the outlets are arranged outside a blank sector of a circumference around the fuel outlet, the blank sector is defined by an angle between and including 30° and 160° about the axis, and

wherein the air from the outlets immediately impinges on the fuel issuing from the fuel outlet and creates an asymmetric pilot vortex of fuel and air.

2. The fuel lance as claimed inclaim 1,

wherein the outlets are arranged outside the blank sector defined by an angle of between 120° and 160° about the axis.

3. The fuel lance as claimed inclaim 1,

wherein the outlets are arranged outside the blank sector defined by an angle of approximately 140° about the axis.

4. The fuel lance as claimed inclaim 1,

wherein there are eight outlets equally spaced about the fuel outlet and between one and three circumferentially adjacent outlets are blocked off to create the blank sector.

5. A burner for a combustor of a gas turbine, the burner comprising:

a body having a surface and an axis, a fuel lance, an igniter and a main air flow passage or passages,

a fuel lance as claimedclaim 1, wherein the outlets and the fuel outlet are located at or near to the surface,

wherein the igniter is at least partly housed within the body and has an end face, the end face is located at or near to the surface,

wherein the main air flow passage is arranged to direct at least a part of a main air flow over the fuel lance and then over the igniter, and

wherein the blank sector has a centre-line and the centre-line is angled between +120° and −120° from a radial line from the axis and passing through the fuel lance.

6. The burner as claimed inclaim 5,

wherein the main air flow passage or passages are tangentially angled relative to the burner axis to create a clockwise or anticlockwise swirl direction of the main air flow, and

wherein the air passages are tangentially angled relative to a fuel lance axis to create a clockwise or anticlockwise swirl direction of the pilot air flow.

7. The burner as claimed inclaim 6,

wherein the main air flow passage or passages and the air passages are both tangentially angled in the same direction to create clockwise swirl direction of the main air flow and clockwise swirl direction of the pilot air flow or to create anticlockwise swirl direction of the main air flow and anticlockwise swirl direction of the pilot air flow, and

wherein the centre-line of the blank sector is angled up to 60° from the radial line from the axis and passing through the fuel lance.

8. The burner as claimed inclaim 7,

wherein the centre-line of the blank sector is angled up to 20° from the radial line from the axis and passing through the fuel lance.

9. The burner as claimed inclaim 7,

wherein the centre-line of the blank sector is angled approximately 0° from the radial line from the axis and passing through the fuel lance.

10. The burner as claimed inclaim 6,

wherein the main air flow passage or passages and the air passages are oppositely tangentially angled to create oppositely swirling main air flow and pilot air flow, and

wherein the centre-line of the blank sector is angled between 0° and 120° from the radial line from the axis and passing through the fuel lance.

11. The burner as claimed inclaim 6,

wherein the igniter is positioned downstream of the fuel lance with respect to the direction of the main air flow.

12. A method of operating a burner for a combustor of a gas turbine,

wherein the burner comprises a body having a surface and an axis, a fuel lance, an igniter and a main air flow passage or passages, a fuel lance as claimed inclaim 1,

wherein the outlets and the fuel outlet are located at or near to the surface, the igniter is at least partly housed within the body and has an end face, the end face is located at or near to the surface, the main air flow passage is arranged to direct at least a part of a main air flow over the fuel lance and then over the igniter, and the blank sector has a centre-line and the centre-line is angled relative to a radial line from the axis and passing through the fuel lance,

wherein the burner further comprises a rotation mechanism arranged to rotate the fuel lance about its axis,

the method comprising:

rotating the fuel lance between a start-up condition and a second condition.

13. The method of operating a burner as claimed inclaim 12,

wherein at the start-up condition the blank sector is angled between +120° and −120° from the radial line and

wherein at the second condition the blank sector is angled between +240° and 0° from the radial line.

14. The method of operating a burner as claimed inclaim 13,

wherein the second condition is any one of the group comprising weak extinction, part-load or maximum load.

15. The fuel lance as claimed inclaim 1,

wherein the fuel outlet is any one of a fuel prefilmer, an orifice or a number of orifices.

16. The burner as claimed inclaim 12,

wherein the fuel outlet is any one of a fuel prefilmer, an orifice or a number of orifices.

17. The method as claimed inclaim 5,

wherein the fuel outlet is any one of a fuel prefilmer, an orifice or a number of orifices.

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